A variety of retina diseases cause vision loss or blindness by destruction of the vascular layers of the eye that include the choroid and choriocapillaris, and the outer retinal layers that include Bruch's membrane and retinal pigment epithelium. Loss of these layers is often accompanied by degeneration of the outer portion of the neuroretina, typically the photo-receptor layer. Variable sparing may occur of the remaining neuroretina composed of the outer nuclear, outer plexiform, inner nuclear, inner plexiform, ganglion cell and nerve fiber layers.
Known prior efforts to produce vision by retinal electrical stimulation used arrays of stimulating electrodes with their ground return electrode or electrodes disposed either entirely on the epiretinal or the subretinal side of the neuroretina. Placement of stimulating and ground return electrodes together in this fashion resulted in inefficient stimulation of the neuroretina because the electrical field was not forced directly through the neuroretina. Resolution was also degraded because of diffuse spreading of each stimulating electrode's electrical field.